DESCRIPTION(Provided by applicant): One of the problems in characterizing the properties of ion channel-linked receptors like NMDA family is that it is difficult to distinguish between changes in agonist affinity and efficacy, because some changes in efficacy also produce changes in EC50 values. The candidate proposes to study the molecular basis of agonist affinity and efficacy by a combination strategy of single-site mutagenesis of selected amino acid residues into cysteine residues, and then treating receptor preparations with sulfhydryl modifying reagents to reduce agonist effects. The differentiation between agonist efficacy and affinity will be determined using partial agonists, where decreases in efficacy can be observed by a decrease in maximal response. The first specific aim will perform single-site mutagenesis on normal NMDA receptors, while the second aim will perform mutagenesis on mutants in the TM3 region where efficacy has already been reduced. These studies will be performed in frog oocytes expressing NMDA receptors.